A method for evaluating the enrichment degree of free hydrocarbons in continental shale oil

Abstract

The present invention provides an evaluation method for the enrichment degree of free hydrocarbons in continental shale oil, the evaluation method comprising the following steps: (1) clarifying the logging response characteristics of the free hydrocarbon-rich layer section, and selecting sensitive parameters for distinguishing free hydrocarbons from solid organic matter; (2) using the layer section data without free hydrocarbons or with low free hydrocarbon content to establish the change trend line of the sensitive parameters in the formation without free hydrocarbons or with low free hydrocarbon content; (3) using the layer section data with high free hydrocarbon content and low free hydrocarbon content to establish the change trend line of the sensitive parameters with the free hydrocarbon content; (4) using the difference between the change trend lines established in step (2) and step (3) respectively, to judge the relatively enriched layer section of free hydrocarbons in the formation. The evaluation method is highly accurate, convenient and quick, makes up for the shortcomings of the traditional evaluation method, and does not exaggerate or miss the real free hydrocarbon-rich layer section.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale oil exploitation, and relates to a method for evaluating the enrichment degree of shale oil, and in particular to a method for evaluating the enrichment degree of free hydrocarbons in continental shale oil. Background Art

[0002] Continental shale oil refers to the liquid hydrocarbons and various types of organic matter that are stored in continental organic-rich shale formations buried at a depth of more than 300m and with an Ro value greater than 0.5%. The focus of continental shale oil exploration in my country is mainly on free hydrocarbons. This is because part of the oil in the reservoir and mudstone is stored in micropores and cracks in a free state, and a small part is adsorbed on the surface of organic matter and rock particles. Under current development conditions, the oil and gas adsorbed on the surface of organic matter and rock particles are basically immobile and difficult to be mined and utilized. Therefore, how much of the organic carbon content in the formation comes from the contribution of free hydrocarbons is one of the issues that geologists are very concerned about, which also directly affects the researchers' evaluation and prediction of the "sweet spot" section of shale oil.

[0003] At present, there are two main evaluation methods for free hydrocarbons in shale oil: one is the organic geochemical analysis method based on rock pyrolysis, and the other is the evaluation method based on well logging data. Among them, the organic geochemical analysis method based on rock pyrolysis has the advantages of mature technology, high analysis accuracy, economic and fast, small sample usage, and easy acquisition. However, it can only be analyzed for specific rock samples. For wells without rock samples, free hydrocarbon S1 cannot be obtained. Therefore, this method is generally only used for systematic sampling and pyrolysis S1 measurement for key exploration wells.

[0004] Evaluation methods based on logging data are also divided into two types: one is to calculate the content of free shale oil based on the oil saturation in shale pores, and the other is to establish a fitting relationship between the free hydrocarbon S1 obtained from the pyrolysis experiment and related parameters, and use the established fitting formula to evaluate free hydrocarbons. Among them, the oil saturation method is the closest to the reserve calculation in conventional oil and gas exploration. However, since the measurement of shale porosity and oil saturation is greatly affected by other factors, many porosity and oil saturation measurement methods have high requirements for cores, such as sample size, sample lamination or fracture development, shale later preservation, shale soluble organic matter content, etc. These factors greatly limit the accurate measurement of shale porosity and oil saturation. In the absence of reliable "core calibration logging" data, the calculation error of shale porosity and oil saturation using logging data is greater, so this method is difficult to implement in reality.

[0005] The current mainstream evaluation method for free hydrocarbon S1 is to fit the free hydrocarbon S1 obtained from the core or cuttings pyrolysis experiment with related parameters, and use the obtained fitting formula to evaluate the free hydrocarbon S1. The commonly used method is to establish a fitting relationship between free hydrocarbon S1 and organic carbon content TOC. This calculation method is easy to use and has a wide range of applications, but it still has certain limitations. In this fitting relationship, as the abundance of organic matter in the formation increases, the content of free hydrocarbons increases accordingly, but the actual situation is not always the case, that is, the amount of free hydrocarbons in the formation does not entirely depend on the abundance of organic matter. This is because solid organic matter (kerogen) can lead to an increase in organic carbon content, but it does not contribute to free hydrocarbon S1. Therefore, simply using the fitting relationship to evaluate the free hydrocarbon S1 content often cannot exclude the influence of solid organic matter, resulting in a larger calculation result, which in turn affects the true evaluation of the "sweet spot" section of shale oil. In addition, the evaluation of organic carbon content TOC currently relies on the calculation of logging data, and there will be errors between the calculated results and the actual core analysis results. Therefore, there is a risk of error transmission when evaluating free hydrocarbon S1 based on the calculated organic carbon content. Only by clarifying the organic carbon content corresponding to the free hydrocarbons or residual solid organic matter in the rock can the organic carbon content be used to accurately evaluate the true situation of free hydrocarbon S1. However, there is no good solution for evaluating the organic carbon content corresponding to the free hydrocarbon part, resulting in the inability to accurately evaluate the true situation of free hydrocarbons in the formation directly using the organic carbon content, which restricts the prediction of the real "sweet spot" layer of shale oil.

[0006] It can be seen that how to provide an evaluation method for the enrichment degree of free hydrocarbons in continental shale oil, improve accuracy and evaluation efficiency, make up for the shortcomings of traditional evaluation methods, and avoid exaggerating or missing the real free hydrocarbon-rich layers has become an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0007] The purpose of the present invention is to provide a method for evaluating the free hydrocarbon enrichment degree of continental shale oil. The evaluation method is highly accurate, convenient and quick, makes up for the shortcomings of traditional evaluation methods, and does not exaggerate or miss the real free hydrocarbon-rich layer section.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for evaluating the enrichment degree of free hydrocarbons in continental shale oil, the method comprising the following steps:

[0010] (1) Clarify the logging response characteristics of the free hydrocarbon-rich interval and select sensitive parameters for distinguishing free hydrocarbons from solid organic matter;

[0011] (2) Using data from layers without free hydrocarbons or with low free hydrocarbon content, establish trend lines of changes in sensitive parameters in layers without free hydrocarbons or with low free hydrocarbon content;

[0012] (3) Using data from layers with high and low free hydrocarbon contents, establish trend lines of sensitive parameters changing with free hydrocarbon content;

[0013] (4) using the difference between the change trend lines established in step (2) and step (3), respectively, to determine the relatively rich layer section of free hydrocarbons in the formation;

[0014] The low free hydrocarbon content refers to a free hydrocarbon content of ≤4 mg / g; the high free hydrocarbon content refers to a free hydrocarbon content of >4 mg / g.

[0015] In the present invention, the low free hydrocarbon content means a free hydrocarbon content ≤4 mg / g, for example, it can be 0.5 mg / g, 1 mg / g, 1.5 mg / g, 2 mg / g, 2.5 mg / g, 3 mg / g, 3.5 mg / g or 4 mg / g, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In the present invention, the high free hydrocarbon content refers to a free hydrocarbon content > 4 mg / g, for example, it can be 4.5 mg / g, 5 mg / g, 5.5 mg / g, 6 mg / g, 6.5 mg / g, 7 mg / g, 7.5 mg / g or 8 mg / g, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] The evaluation method provided by the present invention first constructs a parameter that can indicate the degree of enrichment of free hydrocarbons by utilizing the difference between free hydrocarbons and solid organic matter in logging responses, and then calibrates the parameter using the free hydrocarbon content after depth correction to determine the lower limit value of the parameter. When the parameter value is greater than the lower limit value, the free hydrocarbons in the corresponding layer section are relatively enriched, thereby realizing the use of the constructed indicator parameters to identify the relatively enriched layer section of free hydrocarbons.

[0018] The evaluation method provided by the present invention can also be used when only conventional logging data are available, and is suitable for the rapid identification of free hydrocarbon-rich intervals in medium-to-high maturity continental shale oil formations (organic-rich shale formations with an organic matter maturity Ro>1.0%). It is convenient and fast, and the free hydrocarbon-rich interval indication is accurate. It has good application effect and good generalizability.

[0019] Preferably, the sensitive parameters in step (1) include acoustic wave time difference and compensating neutrons.

[0020] The present invention finds through analysis that the acoustic time difference and the compensation neutron react relatively sensitively to the change of free hydrocarbon content. When the free hydrocarbon content is higher, the acoustic time difference and the compensation neutron increase significantly, and under certain scale conditions, the more obvious the difference between the two curves, the higher the corresponding free hydrocarbon content. Because for free hydrocarbons and solid organic matter, the difference in hydrogen content between the two is not large, but the difference in phase state will be reflected in the acoustic wave velocity, so the two parameters of acoustic time difference and compensation neutron are selected as sensitive parameters.

[0021] Preferably, the method for establishing the change trend line in step (2) is: based on the free hydrocarbon content results of the experimental analysis, corresponding layer data with no free hydrocarbons or low free hydrocarbon content are selected, and a change relationship curve between the acoustic wave time difference and the compensated neutron is established, that is, a change trend line of the sensitive parameters in the formation with no free hydrocarbons or low free hydrocarbon content is obtained.

[0022] In the present invention, the change trend line established in step (2) is used to reflect the change pattern of sensitive parameters of the formation when there is no free hydrocarbon or the free hydrocarbon content is low.

[0023] Preferably, the method for establishing the change trend line in step (3) is: based on the free hydrocarbon content results of the experimental analysis, corresponding layer data with high free hydrocarbon content and low free hydrocarbon content are selected to establish a change relationship curve between the acoustic wave time difference and the compensated neutron, that is, to obtain a change trend line of the sensitive parameters with the free hydrocarbon content.

[0024] In the present invention, the change trend line established in step (3) is used to reflect the influence of the free hydrocarbon content on the sensitive parameters.

[0025] Preferably, the discrimination criterion in step (4) is that the content of free hydrocarbons in the formation is positively correlated with the difference between the two variation trend lines.

[0026] In the present invention, step (4) is to use the change trend lines established in step (2) and step (3) to identify the relatively rich layer section of free hydrocarbons in the formation. Since the change trend line established in step (2) reflects the change law of the acoustic time difference and the compensation neutron in the formation without free hydrocarbons or with low free hydrocarbon content, and the change trend line established in step (3) reflects the change law of the acoustic time difference and the compensation neutron with the change of free hydrocarbon content, therefore, under the same circumstances, the greater the difference between the two change trend lines, the higher the free hydrocarbon content in the formation, so the obtained change trend line can be used to carry out rapid identification of the free hydrocarbon rich layer section.

[0027] As a preferred technical solution of the present invention, the evaluation method comprises the following steps:

[0028] (1) clarifying the logging response characteristics of the free hydrocarbon-rich interval and selecting sensitive parameters for distinguishing free hydrocarbons from solid organic matter, wherein the sensitive parameters include acoustic time difference and compensated neutrons;

[0029] (2) Based on the free hydrocarbon content results of the experimental analysis, the corresponding data of the layer section with no free hydrocarbon or low free hydrocarbon content are selected to establish the change relationship curve between the acoustic wave time difference and the compensation neutron, that is, to obtain the change trend line of the sensitive parameters in the formation with no free hydrocarbon or low free hydrocarbon content;

[0030] (3) Based on the free hydrocarbon content results of the experimental analysis, the data of the layers with high and low free hydrocarbon contents are selected to establish the relationship curve between the acoustic time difference and the compensation neutron, that is, to obtain the trend line of the change of sensitive parameters with the free hydrocarbon content;

[0031] (4) using the difference between the change trend lines established in step (2) and step (3), respectively, to identify the relatively rich layer section of free hydrocarbons in the formation, and the identification criterion is: the content of free hydrocarbons in the formation is positively correlated with the difference between the two change trend lines;

[0032] The low free hydrocarbon content refers to a free hydrocarbon content of ≤4 mg / g; the high free hydrocarbon content refers to a free hydrocarbon content of >4 mg / g.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The evaluation method provided by the present invention first constructs a parameter indicating the enrichment degree of free hydrocarbons by utilizing the difference between free hydrocarbons and solid organic matter in the logging response, and then calibrates the parameter using the free hydrocarbon content corrected by depth to determine the lower limit of the parameter. When the parameter value is greater than the lower limit, the free hydrocarbons in the corresponding layer are relatively enriched, thereby realizing the use of the constructed indicator parameters to identify the relatively enriched layer sections of free hydrocarbons, making up for the shortcomings of the traditional evaluation method and not exaggerating or missing the real free hydrocarbon-enriched layer sections;

[0035] (2) The evaluation method provided by the present invention can also be used when only conventional logging data are available, and is suitable for the rapid identification of free hydrocarbon-rich intervals in medium- to high-maturity continental shale oil formations (organic-rich shale formations with an organic matter maturity Ro>1.0%). It is convenient and fast, and can accurately indicate free hydrocarbon-rich intervals. It has good application effects and is very popularizable. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the logging response characteristic of the shale oil well in the evaluation method provided in Example 1;

[0037] Figure 2is a curve showing the relationship between the acoustic time difference and the compensation neutron in the evaluation method provided in Example 1;

[0038] Figure 3 is a corresponding relationship curve between the measured free hydrocarbon content S1 and the index parameter Z in the evaluation method provided in Example 1;

[0039] Figure 4 It is a scatter plot of the free hydrocarbon content S1 and the organic carbon content TOC measured in the evaluation method provided in Example 1;

[0040] Figure 5 This is a corresponding relationship diagram between the measured free hydrocarbon content S1, organic carbon content TOC and the two-dimensional nuclear magnetic resonance results in the evaluation method provided in Example 1. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0042] Example 1

[0043] This embodiment provides an evaluation method for the enrichment of free hydrocarbons in continental shale oil. Taking the continental shale oil of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin as an example, the lithology of the first section of the Qingshankou Formation is complex, mainly mudstone, including black mudstone (shale), gray-black ostracod-containing mudstone and silt-containing mudstone. There are two types of lithology in the interlayer of the mudstone, namely sandstone and limestone. Among them, high-organic laminar shale and layered shale have the best oil content, with an organic carbon content TOC of 1.0-5.0% and a free hydrocarbon content S1 of 2.0-8.8 mg / g.

[0044] In this embodiment, the evaluation method includes the following steps:

[0045] (1) Clarify the logging response characteristics of the free hydrocarbon-rich interval and select sensitive parameters for distinguishing free hydrocarbons from solid organic matter;

[0046] By comparing and analyzing the logging response characteristics of the intervals with high and low free hydrocarbon content in key wells, it is found that when the free hydrocarbon content is high, the acoustic time difference and the compensated neutron value both increase, and under certain scale conditions (acoustic time difference is based on 140-40 scale, and compensated neutron is based on 45-15 scale), the acoustic time difference curve is on the left side of the compensated neutron curve, and there is a significant difference between the two curves; when the free hydrocarbon content is low, the difference between the acoustic time difference curve and the compensated neutron curve is not obvious, and the acoustic time difference curve may even be on the right side of the compensated neutron curve (see Figure 2). Figure 1 ). Therefore, this embodiment uses the relative change relationship between the acoustic time difference and the compensation neutron to determine the enrichment degree of free hydrocarbons.

[0047] (2) Using data from layers without free hydrocarbons or with low free hydrocarbon content, establish trend lines of changes in sensitive parameters in layers without free hydrocarbons or with low free hydrocarbon content;

[0048] For key wells, based on the measured free hydrocarbon content S1, the acoustic time difference and compensated neutron data of well sections with no free hydrocarbon (Quan 4th section) or low free hydrocarbon content (Qing 3rd section) were selected to establish the change relationship curve of acoustic time difference and compensated neutron. Figure 2 As shown, the dotted line is the relationship curve between the two, which reflects the variation characteristics of the acoustic time difference of the formation with the compensation neutron in the absence of free hydrocarbons or low free hydrocarbon content.

[0049] (3) Using data from layers with high and low free hydrocarbon contents, establish trend lines of sensitive parameters changing with free hydrocarbon content;

[0050] Based on the measured free hydrocarbon content S1, the acoustic time difference and compensated neutron data of the well sections with high free hydrocarbon content and some with low free hydrocarbon content are selected to establish the change relationship curve of the acoustic time difference and compensated neutron. At this time, due to the existence of free hydrocarbons, the change relationship between the acoustic time difference and compensated neutron is different from that in the state without free hydrocarbons, because the hydrogen content of liquid free hydrocarbons and solid organic matter is very high, and the difference between the two in the compensated neutron value is not large. However, the acoustic velocity is relatively sensitive to this phase difference. Therefore, when the compensated neutron value is constant, the smaller the acoustic velocity, that is, the larger the acoustic time difference, the higher the free hydrocarbon content in the formation. Figure 2 As shown, with the change of free hydrocarbon content, there is a nonlinear relationship between the acoustic time difference and the compensation neutron. The solid line is the relationship curve between the two, which reflects the change characteristics of the acoustic time difference of the formation with the compensation neutron as the free hydrocarbon content changes.

[0051] (4) using the difference between the change trend lines established in step (2) and step (3), respectively, to determine the relatively rich layer section of free hydrocarbons in the formation;

[0052] Assume that the change relationship between the acoustic time difference and the compensation neutron obtained in step (2) is DT1=a×CNL+b, where a and b are coefficients of the fitting formula; the change relationship between the acoustic time difference and the compensation neutron obtained in step (3) is DT2=c×CNL 2 +d, where c and d are the coefficients of the fitting formula. The above two fitting formulas are used to calculate the acoustic time difference values ​​DT1 and DT2 that vary with depth, respectively. Let Z be the free hydrocarbon indication parameter, and Z = DT2-DT1. This operation is to eliminate the influence of normal shale on the acoustic time difference and compensating neutrons, and highlight the role of free hydrocarbons. If the Z value is larger, it means that under the same compensating neutron value, the difference in the acoustic time difference value is greater, indicating that the free hydrocarbon content in the well section in the formation is high, that is, relatively enriched. Figure 3As shown, the indicator parameter Z has a good correspondence with the relative enrichment interval of free hydrocarbons (the index parameter Z and the free hydrocarbon content S1 are both 6-20 scales, only to highlight the high S1 value development interval). Therefore, this embodiment uses the indicator parameter Z to determine the development position of the free hydrocarbon-rich interval in the formation. If the Z value is larger and the vertical distribution is more continuous (the thickness of the Z value continuously greater than 6 is larger), the free hydrocarbon is more enriched and the result is more reliable.

[0053] In this embodiment, the low free hydrocarbon content refers to a free hydrocarbon content of ≤4 mg / g; the high free hydrocarbon content refers to a free hydrocarbon content of >4 mg / g.

[0054] Comparative Example 1

[0055] This comparative example provides an evaluation method for the free hydrocarbon enrichment degree of continental shale oil. Taking the Qingshankou Formation shale oil reservoir in the Songliao Basin as an example, a fitting relationship is established using the free hydrocarbon content S1 and organic carbon content TOC measured by multiple wells, that is, S1=0.6614×w(TOC)+1.5269.

[0056] Figure 4 It is a scatter plot of the measured free hydrocarbon content S1 and the organic carbon content TOC in the evaluation method provided in this comparative example. It can be found that compared with well B, the organic carbon content TOC of well A is not as high as that of well B, but the free hydrocarbon content S1 is higher than that of well B, indicating that the free hydrocarbon content in the formation is not entirely determined by the abundance of organic matter.

[0057] Figure 5 It is a corresponding relationship diagram between the measured free hydrocarbon content S1, organic carbon content TOC and two-dimensional nuclear magnetic resonance results in the evaluation method provided in this comparative example, wherein the two-dimensional nuclear magnetic resonance results are measured for the rock samples in a dried state. It can be found that for samples with high TOC and low S1, obvious solid organic matter (kerogen) can be seen in the two-dimensional nuclear magnetic resonance. The presence of kerogen leads to a higher measured TOC value, but a very low S1 value. For samples with no obvious solid organic matter in the nuclear magnetic resonance images, the relationship between their free hydrocarbon content S1 and organic carbon content TOC is obviously different from that of samples with solid organic matter. This further illustrates that solid organic matter can lead to an increase in the organic carbon content TOC, but has no contribution to the free hydrocarbon content S1.

[0058] It can be seen that the evaluation method provided by the present invention avoids the traditional misunderstanding that the higher the organic carbon content, the higher the free hydrocarbon content, and improves the identification of free hydrocarbon-rich layers in shale oil formations. First, by utilizing the difference between free hydrocarbons and solid organic matter in logging responses, a parameter that can indicate the degree of free hydrocarbon enrichment is constructed, and then the parameter is calibrated using the free hydrocarbon content after depth correction to determine the lower limit of the parameter. When the parameter value is greater than the lower limit, the free hydrocarbons in the corresponding layer are relatively enriched, thereby achieving the use of the The constructed indicator parameters are used to identify the relatively rich layers of free hydrocarbons, which makes up for the shortcomings of traditional evaluation methods and does not exaggerate or miss the real free hydrocarbon-rich layers. In addition, the evaluation method provided by the present invention can also be used when only conventional logging data are available, and is suitable for the rapid identification of free hydrocarbon-rich layers in medium-to-high maturity continental shale oil formations (organic-rich shale formations with organic matter maturity Ro>1.0%). It is convenient and fast, and the free hydrocarbon-rich layers are accurately indicated. It has a good application effect and is very popular.

[0059] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for evaluating the enrichment degree of free hydrocarbons in continental shale oil, characterized in that: The evaluation method comprises the following steps: (1) clarifying the logging response characteristics of the free hydrocarbon-rich interval and selecting sensitive parameters for distinguishing free hydrocarbons from solid organic matter, wherein the sensitive parameters include acoustic time difference and compensated neutrons; (2) Based on the free hydrocarbon content results of the experimental analysis, the corresponding data of the layer section with no free hydrocarbon or low free hydrocarbon content are selected to establish the change relationship curve between the acoustic wave time difference and the compensation neutron, that is, to obtain the change trend line of the sensitive parameters in the formation with no free hydrocarbon or low free hydrocarbon content; (3) Based on the free hydrocarbon content results of the experimental analysis, the data of the layers with high and low free hydrocarbon contents are selected to establish the relationship curve between the acoustic time difference and the compensation neutron, that is, to obtain the trend line of the change of sensitive parameters with the free hydrocarbon content; (4) using the difference between the change trend lines established in step (2) and step (3), respectively, to identify the relatively rich layer section of free hydrocarbons in the formation, and the criteria for identification are: the content of free hydrocarbons in the formation is positively correlated with the difference between the two change trend lines, the change relationship between the acoustic time difference and the compensation neutron obtained in step (2) is DT1=f1(CNL), and the change relationship between the acoustic time difference and the compensation neutron obtained in step (3) is DT2=f2(CNL), let Z be the free hydrocarbon indicator parameter, and Z=DT2-DT1, use the indicator parameter Z to identify the development position of the free hydrocarbon rich layer section in the formation, if the Z value is larger and the vertical distribution is more continuous, the free hydrocarbon is more enriched; The low free hydrocarbon content refers to a free hydrocarbon content of ≤4 mg / g; the high free hydrocarbon content refers to a free hydrocarbon content of >4 mg / g.

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